Vernonia amygdalina (Delile) exhibits in vitro anti-plasmodial activities against Plasmodium knowlesi

Malaria is a global public health concern, where Plasmodium knowlesi contributes to most human malaria cases in Malaysia. The leaves of Vernonia amygdalina (Delile) were found to exhibit significant anti-plasmodial properties and are commonly used in sub-Saharan Africa countries for malaria treatment. Nonetheless, studies are lacking in the effect of this plant against P. knowlesi specifically. This study aimed to investigate the in vitro anti-plasmodial activity of crude extracts from V. amygdalina (Delile) against P. knowlesi. The fresh leaves of V. amygdalina were sequentially extracted in three solvents, dichloromethane (DCM), methanol (MeOH) and water (H₂O) to attain the crude extracts. Schizont maturation inhibition assays were performed using in vitro P. knowlesi culture (A1H1) to evaluate the anti-plasmodial activities. The in vitro cytotoxicity of the plant extracts was also evaluated with Vero cell line using MTT assay. Plant extracts in all solvents showed good to moderate anti-plasmodial activity against P. knowlesi, with concentration of drug required for 50% growth inhibition (IC₅₀) of 1.356 ± 0.23 μg/mL, 1.131 ± 0.16 μg/mL and 1.973 ± 0.30 μg/mL for DCM, MeOH and H2O extracts, respectively. The concentration of drug that is cytotoxic to 50% cell populations (CC₅₀) for each extract is DCM = 48.61 ± 0.64 µg/mL, MeOH = 63.73 ± 0.78 µg/mL and H₂O = 86.91 ± 1.03 µg/mL, indicating the MeOH and H2O extracts were likely non-toxic to the mammalian cells. In the present study, all crude extracts exhibited Selectivity Index (SI) values above 10, with MeOH extract having the highest selectivity towards malaria parasites. These findings suggest that the extracts of V. amygdalina leaves exhibit anti-plasmodial properties against P. knowlesi even in the crude form and may be a potential candidate for the development of new antiplasmodial drug. This provides scientific evidence for usage of this plant in traditional medicine, and further studies are needed for identification and purification of the active metabolites.